1. Field of the Invention
The present invention relates to an electrophotographic printing apparatus having a photosensitive member electrified in a printing operation, and more particularly to an electrophotographic printing apparatus wherein unnecessary electrical charges are removed from the photosensitive member before the next printing operation.
2. Description of the Related Art
In the general electrophotographic printing apparatus, the surface of a photosensitive member, which is formed of photoconductive material, is evenly electrified and selectively exposed by light radiated in accordance with input image data. Thus an electrostatic latent image is formed on the surface of the photosensitive member. Then, toner, which adheres to the surface of the photosensitive member in accordance with the electrostatic latent image, is fed to the surface of the photosensitive surface, so that the electrostatic latent image is developed. Then, a sheet of paper is charged and a toner image is transferred to the sheet of paper from the surface of the photosensitive member by electrostatic attraction. After the image transfer, the toner image is fixed to the paper sheet by heat and pressure, and the paper is discharged. On the other hand, the photosensitive member is processed to remove toner which withstands the electrostatic attraction and remains on the surface. The photosensitive member then processed to remove unnecessary electrical charges.
An EEH (edge emitter array head) type electrophotographic printing apparatus comprises a line head positioned in the vicinity of the photosensitive member and has an array of edge light-emitting elements arranged by one row. The photosensitive member is exposed for one line each time these light-emitting elements are selectively driven. The light-emitting element is formed of a light-emitting diode, a semiconductor laser, or an EL (electroluminescence) element, for example. The light-emitting diode and the semiconductor laser have an output characteristic which depends on the environmental temperature. Therefore, the light-emitting diode and the semiconductor laser are controlled in accordance with the change of the environmental temperature so as to keep the output constant in the printing operation. However, such a control is not effected in the EL element, whose an output characteristic does not substantially depend on the environmental temperature.
In the conventional electrophotographic printing apparatus, even if the output of the light-emitting elements is not changed, the printing quality can still deteriorate. This deterioration of the printing quality is caused by the change is deelectrification efficiency caused by the environmental temperature of the photosensitive member. For example, when the environmental temperature of the photosensitive member is low, necessary electrical charges are not completely removed from the photosensitive member. Due to this, the potential of the deelectrified photosensitive member is increased, and the sensitivity of the photosensitive member is decreased. Because of the decrease in sensitivity of the photosensitive member, the line elements of the electrostatic latent image to be drawn on the surface of the photosensitive member become thinner and the printed characters and drawings thus become unclear.